Coded track circuit signaling system



June 6, 1944.

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CODED TRACK CIRCUIT SIGNALING SYSTEM Filed Sept. 29, 1942 16 Sheets-Sheet I4 uw m Patented June 6, 1944 CODED TRACK Cg CUIT SIGNALING Neil-D; Preston, Rochester, Y., assignor to eneral Railway SignalCompany, Rochester,

Application September 29, 1942, Serial No. 460,106

40 Claims. I (01. 246-33) This invention relates to coded track circuit signaling systems for railways, and more particularly to an automatic block signaling system for single track railroads.

In one type of automatic block signaling sys- ,1

tem for single track railroads, commonly known as the absolute-permissive-block or A. P.'B. system, the signals governing train movement into and through each singl track stretch between passing sidings' are normally clear to permit trains to enter the stretch at either end in accordance with train orders or time table rights. When a train enters a single track stretch, the opposing signals are automatically put to stop by an operation conveniently termed a tumble-down control; and as th train travels through the stretch and passeseach intermediate signal, a directional means is conditioned to permit clearing of the signals for following train movements independently of the tumble-down control. In addition to this tumble-down and directiona1 contro1 for the signals of the single track stretch, the entering signals governing. train movement into a passing siding and its associated siding section, and each of the intermediat signals in the rear of these entering signals, are governed in a special way to provide what is commonly known as a double distant and siding overlap control in the manner and for the purposes familiar to those skilled in the art.

The primary object of th present invention is to provide an automatic block signal system for single track railroads of the absolute-permissiveblock type which is operated by the coded track circuits without any line wires between signal 10- cations, and which affords all of the signaling protection for opposing and following train movements characteristic of the well-known A. P; B. system using conventional track circuits and line wires.

In the conventional coded trackcircuit; the

track rails at one end of a track section are intermittently energized to form code pulses for operating a code following'track relay at the other end of the track section, unless a track section is occupied by a train; and by changing the rate or periodicity of these code pulses, or, otherwise varying their cod character, distinctive controls 'may be transmitted over the track rails for governing the indication of wayside or cab signals without the use of line wires.

In applying such coded track circuits to an automatic block signalingsystem of the a'A P. B. type, it becomes necessary to provide for suitable code control over the track rails of the track sec:

tions in both directions to provide for clearing the starting or head-block signals at both ends of the single track stretch when this stretch isnot occupied, thereby allowing a train to enter the stretch at either end under a clear signal when trafiic conditions permit, and also provide for a tumble-down control for both directions to put to stop opposing signals when a train enters the stretch. This desired code control for both directions in the track sections of a single track stretch under normal conditions maybe obtained by using a driven code for one direction and an inverse or ofi-code for the opposite direction, as disclosed in my prior application, Ser. No. 413,021, filed September 30, 1941. Also, a code control in both directions in 'a track'sect'ion for detection of occupancy and tumble-down control may be obtained by applying what may be termed the beat code principl as disclosed, for example, in connection with a coded track circuit signaling system having supervisory manual control, in the prior application of Judge, Ser. No. 455,922 filed Aug. 24, 1942.

In accordance with the present invention, it is proposed to employ the beat code principle disclosed in this Judge application, Ser. No. 455,922, rather than driven and inverse codes disclosed in my prior application, Ser; No. 413,021, for the control of th signals in an automatic A. P. B. system; and although the present invention involves functions and structural organizations similar to those disclosed in'these prior applications, no claim is made herein to any of the features disclosed in these prior applications.

Generally speaking, and without attempting to define the nature and'scope of this invention, ach track section is equipped with a code transmitting means including coding contacts operated by a code oscillator or equivalent coder device; and under normal conditions these transmittin means for'the opposite ends of the same track section are governed by coding contacts operated at difierent rates, such as and times per minute, thereby providing beat code pulses alternateiy'in opposite directions over the track rails of the track section to cause intermittent energization of the code following track relays at both ends of that track section. Such intermittent energization of the track relays by heat code pulses maybe utilized to detect occupancy and provide tumble-down control, since the energization of a track relay will cease if the track section becomes occupied, or ifthe opposingcode pulses are cut off by a tumble-down control from an adiacent track section; butsuchintermittent been received at a head-block signal without in'-' terference, and cause that signal to indicate clear,

whereupon the opposing code pulses at the appropriate different rate are applied to establish beat code conditions, and the clear indication of the signal once establishedis then maintained'so' long as code pulses are being received at that signal regardless of their particular rate.v

Stated more specifically, the system of this ine vention employs a distant relay for each head-- bioe si a z which is en rgized by n so a de odin neens only whe the o r p d g n e io low ne t aok. re ay i inte m tte t en rsiz dnt a pr determi ed clear o e rate, su a .12 ode u sesper minut a d his d ta re- .l y when on e. ene i ed causes h app cation o code. ulses to c ea a po tcod ndition,

an s ma nta n d ener i ed. by a t ck c rc it or "e iva en means so lon as he ss iated. home :reie is ene i ed by an in erm ent operation of the. c r espondin rac e ay at, recurrent inte vals under-the. b at. ode conditi ns. Under o her onditions when bot the di tant. re ay and h h me r lay are, d eners z by the mblei wn control. u to t e presenc of a rain n a s retohmov ns towardthe headslock signal. cod pulses t a code rate deteini n dbytrafiio; e ndi :t o s. a e s p ed f r o n ng e nd cati n of .the inte mediat ignal go r ing train movement towar s idhea mio k s sna V f In. th presen i e tion. th s me heat co pr noi le. is eisoveni ye th. special ont ol, in the manner similar to that disclosed. in my 1 .0 .atii ieat on v Sen N .1 .0 1 abo e ne tioneiatorr vi e With ut se or i e ires he .doubi 't istant eniis dine ov lap. con o haracteristi .o th APE-B.- syst nt Ano her ob ct oit iis invent on. s to provid suitable automatic control ofa swtich loclg for an outlying switch so as to preventthis switch from bei unlos e encior edw a r n s enproaching in either direction, and still permit the switch'to be unlocked and operated with fability for a train movement from the main track over the switch.

Inasmuch'ps' most' railroads have highway crossings at grade level, it is another object 'of the present invention to provide ano'vel and simple means for controlling highway crossing signals automatically upon the approach of a train in either direction "over single" track stretches in such a manner as to readily effect the stopping of the highway 'crossing'sig'nal in its warning operationas soon as a train passes such highway.

functions and structural organizations constituting the invention will be set forth in the appended and arrangement of parts preferably employed in j practice. These drawings comprise a number of figures as follows:

Figs. 1A, 1B, 1C and 1D, adapted to be arranged end'to end, illustrate one embodiment of the in- Although one purpose of the invention 'is'to provid'e such highway crossing protection which is particularly suitable to the signaling system dis closed herein, it'is also an object of the invention vention of this system as applied to a typical stretch of single track between the ends of passing sidings, and as applied to a typical one passing siding and associated siding track section when Figs; 11) and 1A are placed end to end in that lid traclgsections and the control of the si nals for certain typical tra ir 1 movements;

.E'igs 3A and 3B illustrate a modified arrangement of the control circuits for governing the intermediate signalsv associatedv with the middle track section ofa single track stretch;

Figs. 5l and 5 show conventionally ancldiagrammatically different specificembodiments of the automatic control of a switch lock for an outlying switch in accordance with this invention;

Figs. 6A 63 and 6C, placed end to end, show conventionally and diagrammatically one specific embodiment of a highway crossing control system of the typerparticularly adapted for usewith the .coded track circuitautomatic APB system of this .i YQ tiQ v Figs. 7A to 7F inclusive constitute a series of explanatory diagrams, illustrating different, conditions of coding for. certain typical trainmove- .nient nest h hig way cr ssing of Fi s. 6 6 a d. QC; and

Fig. dis a diagrammatic illustration Of the manner in which beat code impulses are formed by the combination of two independently operable coders operating at difierent rates and located at the opposite ends of the track. section .1441: strewn- B- V I Thevarious relays, contacts and other Parts have" been illustrated in these, drawings in a conyentional manner; and to simplify the illustration 'of'the circuits'connections to theopposite terminals of the battry or other'suitable source of current for energizing the local circuits have beenrepre's'entedby the symbols and associated with arrows. A system of this type inherently involves a similarity and duplication of relays and like parts] for the different signal 10- cations; and for simplicity various relays common to the various signal 'locations are. assigned the same reference letter with'a prefix numeral corresponding to] the signal. In many instances, the same arrangementof control circuits isemployed' for energizing corresponding relays'associ'ated with the different signal locations, so that a description of the circuits and mode oioperation for one typical signal location applies to all signal locations; and while there are. corresponding'contacts in many cases at the different. signal locations; these contacts will' be designated by different reference'numbers in order as the oper tween the ends ofpassing sidings, togetherwith passing sidings and associated siding track sections constituting the portion of the main track opposite these passing sidings. I It has also been assumed that the passing-sidings are not equipped with track circuits. The switches'AW and BW at the ends of the-passingsidings are arranged to be operated manuallyby thetrain crew in accordance .with the usual practice: and it is assumed. that the-switches will be equippedwith suitableswitch circuit controllers-(not shown) for governing thecoded track circuits and signals in accordance with the usual practice. j a

Figs. 1A to 1D inclusive, when arranged end to end, illustrate the apparatus and circuits for a single track stretch between siding ends A and B, with starting or head-block signals l and 8 governing east-bound and west-bound train movement respectively into the stretch, entering signals 2 and l governing west-bound and east bound train movement respectively out of the stretch into their corresponding passing siding or associated siding track section, and two pairs of opposite intermediatesignals 3, 4 and;5, 6 governing train movements in the .opposite directions through the stretch. These signals maybe of any suitabletype; butforsimplicity in the illustration of their control circuits, these signalsare assumed to be color-light signals which display green, yellow and red lights for clear, caution and stop indications when the lamps G, Y and R are lighted by the circuits shown. In accordance with usual practice, the head block signals l and 8 are arranged to display, an absolute stop-and? stay indication, while the other, signals are ar ranged to display permissive stop indications, such as by the vertical orstaggered relation of the signal light with a marker light (not shown). 3 In the particular arrangement shown, provision is made for approach lighting the enterin signals and intermediate signals; and if the passing-sidings areprovided with track circuits, the head-block signals may also be approach lighted, instead of normally lighted as shown. The indications of these signals-are governed by home relays, H and distant relays D; audit is evident that these two relays maybeemployed in accord ance with established practice for governing semaphore signals, or other types of color light signals, such as the so-called search-light signal disclosed in thepatentto Field, No. 2,097,785,

November 2,1937. 1 r 1 Each of the siding track sections opposite a passing siding and eachtrack section or block between successive signals is provided with coded track circuit equipment similar to, and involving the same operating principles as the conventional andwel-known codedtrack circuit. This coding equipment is substantiallyv the same'for each end of each track section, andv comprises a, source ofcurrent (assumed to be a battery), a code following, track relayTR, a code transmitter relay C and coding contacts intermittentlyoperated at predetermined code rates -;by acode oscillator or equivalent power operated device, these coding contacts being designated 15CT, l 2llQT;and IBUCT corresponding with code rates of 75, 12,0 andl80; times per minute selectedas suitable for this invention, although it should be understood that other specific code rates may be employed. Each code transmitter relay CTP is arranged to be operatively connected under the various trafi'ic conditions to appropriate coding contacts; and when this transmitter relay is energized and deenergized it connects the source of current and the trackrelay respectively across the track rails alternately at a rate determined by the coding contacts to which thetransmitter relay is thenconnected;

Each track relay TR governs the energization of a decoding transformer in the usual Way to cause the energization of a home signal control relayH while the track relay is intermittently energized at recurrent intervals, regardless of the particular rate of such intermittent energization. aThis decoding transformer also governs the energization of a distant signal control relay D by atuned circuit and rectifier, so that this distantrelay D is energized in response to the coding operation of the track relay TR at a predetermined clear code rate, all in a manner that will be readily apparent to those skilled in the art Without further explanation.

.In the specific embodiment of the invention shown in Figs. 1A to 1D, inclusive, the code rate V is used for the caution signal indication and the code rate for the clear signal indication, ex,- cept in the case of entering signal! (see Fig. 1D) where the clear indication is given when the distant relay 1D is energized by a code of the code rate, and the caution indication either bya 75 code energizing the home relay ll-I alone, or 120 code energizing a special distant signal control relay 'IDX as well as the home relay 7H. This caution control of the entering signal! by different 75 and 120 code rates is employed in connection with the control for a conditional double distant indication in the manner later explained. Each of the code following track relays TR, although illustrated conventionally as a neutral relay, is preferably of the two-position biased polartype and responsive to one polarity of energization only as indicated by arrows; and the polarities to which these track relays will respond and the polarities of the track batteries-are chosen for the several track sections so that each'track relay is not operable by its associated track battery, nor by the track battery on the opposite side of the associated insulated joints. In other words, the polarities are preferably staggered in a well-known manner to provide broken down joint protection. Similarly, the code transmitter relays CTP are preferably of the two-position biased polar type for quick operation, while the other relays of the system are of the usual neutral type, some equippedwith copper slugs or shunting rectifiers so as to have the desired slow-release characteristics. 7

Also associated with each signal, except the entering signals 2 and 1, is a series or approach lighting track relay SR, its slow-release repeater relay SRP, and a directional stick relay S. The series relay SR is connected in series with the track battery and adapted to be intermittently energized when the corresponding transmitter relay CTP is energized while the corresponding track section is occupied by a train, due to the increase of current through this series relay SR caused by the wheel shunt of the train. The series repeater relay SRP is suificiently slowreleasing. to hold its contacts closed although its series relay SR'is intermittently energized, Each;

of the directional stick relays S is arranged to be energized by circuits later explained only. if a train moves: in the directionof traflic governed by the associated signal, and is maintainedenergized'so long as such train-occupies the track section in advance of said ignal.

It has been assumed that the coded track circuitswlll be of the conventional direct current type using primary batteries, or storage batteries trickle-charged from a suitable power line in accordance with commonpractice; but it should 'be appreciated that the same features and operating principles of the invention may be used in connection with coded'track circuits energized by alternating current, or a half-wave of alternating current, or in any other suitable manner.

Under these normal conditions, code pulses (conveniently termed beat code pulses) are being transmitted in both directions in each track section to energize intermittently both of the trackrelaysfor that track section. Generally V speaking,- this beat code condition is produced by governing the transmitter relays CTP for the opposite ends of the same track section by coding contacts operating at difierent code rates, such is '75 and 120 times per minute, each transmitter relaybeing preferably arranged to be energized upon closure of its associated codingcontacts only if the corresponding track relay TR is then deenergized. In the caseof the end track sections l- -4T and 5-8'I' in Figs. 1A and 1D, the transmitter relays 401? and 501? providing code pulses and operating the track relays ITR and 8TH, associated with the corresponding headblock signals l and 8, are normally-governed by coding contacts [2001' operating at the clear code rate, while the transmitter relays ICTP and 8C'I'P'at the opposite ends of these end track sections are normally governed by coding contacts 1501- operating at the caution code rate. In this instance, the selection of the direction for the transmission of code pulses at the higher code rate is necessary to provide the required clear indications of the head-block signals l and 8; but the selection of direction for transmitting code. pulses at the higher code rate in the other track sections is a matter of arbitrary choice. In the arrangement shown, as a matter of choice, the higher 120 code rate is used for transmission of code pulses west in the siding track section 1-2T and inthe middle track section 3-6T. The directionlof the beat code pulses and the rate of their governing coding contacts is indicated in the diagram of Fig. 2A, the dotted line arrows being used to distinguish beat codes from driven codes indicated by solid arrows in the diagrams of other. figures, such as Fig. 23. It is to be understood that the actual rate of the beat codepulses in any track section is a combination of the two, different rates of the governing coding contacts at the opposite ends of that track section and the resulting rate has not been indicated in the diagram'of Fig. 2A.

7 Considering now more in detail the so-called beatcode conditions in a track section, and referringito-the track section i-4T in Figs. 1A and lBas typical, and: further disregarding for the present how. these normal conditions became established, the transmitter relay IC'I'P (Fig. 1A) is connected to coding'conta'cts I5CT by a circuit which maybe tracedlfrom through a back contact 20 of track relay ITR, 'codin'g 'contacts 'ISCT; front contact 2| ,of the distant relay ID, transmitter relay ICTP, and back contact 22 of the directional stick relay lS,-to.('); The transmitter relay'4CTPfor the otherend o'f'this track section (Fig- 1B) is connected toc'oding contacts |20CT bya similar circuit from (-1-); through a back contact'23 of the'track relay 4TR, coding contacts I20CT,.Iront contact 24 of home relay 3H, transmitter relay '4CTP,and back contact25 of directional stick relay 43. 1 I I Thus, the transmitter relays lCTPand ACTP for 'the-opposite ends'of this track -"section l-4T are energized from coding contacts operating at different code-rates subject to the deenergized condition orthe corresponding trackrelay; and the net effect is to provide code pulses-of slightly variable duration and time spacing-alternately in opposite directions, as shown by the diagrams of Fig. 8. For example, if the coding contacts T governing the transmitterrel'ay [CTP are closed at a given-instant while the coding contacts |20CT governing the other transmitter relay 4CTP are open, so that the track relay ITR is deenergized, then at this instant the transmitter relay I CTP becomes energized and applies the track batteryto the corresponding end of the track section and" energizes the track relay 4TB at the other end; and when-this code pulse ceases, the-transmitter-relay 4CTP' at said other end may be energized to apply a battery atthat end to energize the trackrelay ITR. Since the coding contacts governing these transmitter relays are operated at difierent rates, they act to close the energizingcircuits for these transmitter relays at difie renti'ntervals and tend to provide code pulses'at these difierent intervals in opposite directions." i

In the preferred arrangement shown, each transmitter relay cannot be energized, regardless of the closure of its associated coding contacts, until the code pulse from the opposite end of the track section ceases, and its associated track relay becomes deenergiz'ed. Consequently; a transmitter relay CTP cannot operate todisconnect its track relay-from the track rails and cut short its energization bya code pulse being applied at the opposite end of the track section. In other words, the e'nergi'zation' of a track relay initiated during the ofi" period of the associated codingcontacts is r'na'intained for the'full' duration of the code pulse from the opposite end, and is not unduly curtailed by a subsequent closure of its associated coding contacts. Thus, although intermittent energization of both of the track relays of a track section can be produced by transmitter relays governed directly by coding .contacts operating at-difierent code rates independently of the energized condition of the corresponding track relay, and may beused with this invention if desired} the control of each transmitter relay by the back contact of its "associated track relay in the manner shown is preferred, because itserves to provide track relay energizations of more uniform duration.

Another important aspect of the control of each transmitter relay CTP by the back contact of its associated traclirelay is the protection aiforded against false self-coding operation" in the eventof foreign current'on-the track rails.

Suppose, for example, that a stray potential ex- 

